How to replace the head gasket on a lawnmower, step by step


Does your lawnmower run but make a funny puffing sound? Does white smoke come out from the muffler or even from the engine itself? Power dies out after starting the engine? All these problems are pointing to a head gasket problem. Replacing your head gasket is a more complex repair, but this blog’s step-by-step approach will help you finish it with a positive result if you are up to it.

How to replace the head gasket on a lawnmower, step by step:

  • Step 1: Gather all required tools and Take safety precautions
  • Step 2: Lift the engine cover off
  • Step 3: Remove the carburetor, filters, and dipstick from the engine
  • Step 4: Find and remove the sparkplug
  • Step 5: Open up the engine head
  • Step 6: Note the scuffs, scratches, or marking or blows around the head
  • Step 7: Check for carbon deposits of valves and piston
  • Step 8: Clean the exterior surface of the head and valve cover
  • Step 9: clean piston head and hone any scratches from the liner
  • Step 10: clean the surface below the gasket
  • Step 11: Reinstall new gasket
  • Step 12: Reassemble all the components
  • Step 13: Start the lawnmower and check if any problem persists
How to replace the head gasket on a lawnmower, step by step 1

Purpose of the head gasket, engine compartments, and failure causes

A head gasket is a seal that is present between the engine head and cylinder. To have a better understanding of the repair itself, we will first start with where the head gasket is located and what the purpose is:

● Where is a lawnmower head gasket located:

TheHead gasket is located between the engine head where the valves and sparkplugs (mostly) are present. The Head gasket is made from a layered material and has a specific cut geometry, so it fits perfectly. The Head gasket avoids the entrance and exit of fluids and pressure inside the engine cylinder block.

● What is the purpose of a lawnmower head gasket:

Whenever a fluid pipeline is made, be it gas supply, water supply, or even tubing inside a coffee machine, all of them have seals or rings present at joints. The purpose of any seal is to avoid leakages and losses. These seals are usually were easy to replace and do not require any attention to detail. However, the head gasket is an essential component because its purpose is not to contain any simple fluid but keep the engine running in good condition. It serves the purpose of holding the high pressure of fuel combustion as well.

● Lawnmower engine compartment and working cycle

Lawnmowers usually have internal combustion engines running on gasoline or diesel. In both cases, operating pressures inside the machine are very high. The piston compresses the fuel-air mixture for fuel to combust, and then this compressed mixture is burnt. The chamber in which the piston moves up and down is called the cylinder liner. The cover in which intake and exhaust valves are present is called the head. Between these two compartments, a gasket is placed.

Engine valves are present in the head, and a Cam mechanism makes sure the inlet of air and fuel, and exhaust occurs at the required time during the cycle of four steps. These four steps are intake, compression, power, and exhaust.

● Failure of a lawnmower Head gasket: Causes and Effects

The importance of the head gasket and its functionality has been explained. The Head gasket has to bear a very high range of pressure, but it also has its limits. If the engine timing is out and misfires or knocking occurs, high forces beyond normal are produced. The gasket becomes weak and, in some cases, blows completely.
There are several symptoms and signs that can be a result of a blown or damaged head gasket:

  • Blue or white smoke
  • Puffing sound while starting
  • Oil leak and splashes
  • Oil and coolant consumption
  • Foamy or milky coolant
  • Total failure to start

If a head gasket failure is left untreated it can cause engine damage.

Step by step guide to replacing the lawnmower head gasket

● Step 1: Gather all required tools and Take safety precautions

Tools Required: Before getting to work, it is essential to arrange all the required equipment. The main tools include:

  1. Socket wrench
  2. Wire brush
  3. Sandpaper
  4. Engine cleaner
  5. Rag
  6. Collector pan
  7. Grip pliers
  8. Clips/ stopper

Precautionary Measures: These are some things you should be aware of when carrying out this specific repair.

  1. Use safety goggles and gloves to protect yourself as well as delicate engine parts and surfaces from scratches
  2. Try to carry all task in the open air and away from fire sources
  3. Try not to overtighten any bolts, and it will lead to permanent damage to threads
  4. If using compressed air for blowing particles of dirt and carbon, use safety and try to keep pressure nominal
  5. Gap the sparkplug before checking
  6. Use only the gasket specified in the manual or on the engine and match to the old one for size.

● Step 2: Lift the engine cover off

Whenever working on a lawnmower engine, the first step is to remove the covers to better access the engine and related components.

  • Step 2.1: Start by locating the bolts and checking for the socket size.
  • Step 2.2: Using a socket wrench, remove the bolts
  • Step 2.3: If the cover is not spring-loaded, just 2 to 4 latches of grooves will be holding it. Remove by pulling the body off
  • Step 2.4: Look for any electric connection with hood fan or light and remove it from the allocated connection clip

● Step 3: Remove the carburetor, filters, and dipstick from the engine

Before opening the engine head, it is vital to all the complementary parts present over the engine.

  • Step 3.1: Locate fuel supply line, carburetor, oil pump, and filter and oil pipes
  • Step 3.2: Start by removing the fuel line. Clip the pipe or close using a stopper
  • Step 3.3: Look for the carburetor connection, remove it along with its gasket, and keep the screws safe.
  • Step 3.4: Remove the oil filter, pump connection, and pipe going to the oil sump from the engine
  • Step 3.5: If the engine has a cooling system remove those pipes as well
  • Step 3.6: Take the precaution of putting rag or collector pan while performing these to avoid spills all over the place

● Step 4: Find and remove the sparkplug

The next step is to locate the sparkplug wire and disconnect it. Unscrew the sparkplug using a torque wrench.

● Step 5: Open up the engine head

The engine head is usually bolted down onto the main engine block. The easiest way to locate it is the surface on which the sparkplug was placed.

  • Step 5.1: Locate and Unscrew the bolts present on the valve cover
  • Step 5.2: Put a rag or collector pan below to collect any lubricant oil present in the head
  • Step 5.3: Please take a look at both the valves and their respective pushrods. This step is very crucial
  • Step 5.4: Remove the pushrod and rocker mechanism smoothly and carefully
  • Step 5.5: Unscrew the screws present around the head of the engine and pull it off carefully
  • Step 5.6: Clean any spills of fuel or lubricant 

● Step 6: Note the scuffs, scratches, or marking or blows around the head

There are usually three signs of a blown gasket.

  1. Any blown scuff present around the area covered by the gasket
  2. Blown away or cracked layer of the gasket itself
  3. Marks of oil or coolant seepage into the tank

● Step 7: Check for carbon deposits of valves and piston

The inside of valves and the piston’s top is the place where most of the oil deposits. Black-colored lumps are usually present, and these can be fatal.

● Step 8: Clean the exterior surface of the head and valve cover

Use some spare gas and paintbrush or wire brush to clean the outer surfaces.

● Step 9: clean piston head and hone any scratches from the liner

  • Step 9.1. Piston top dead center: Turn the flywheel to bring the piston to the top dead center, i.e., the topmost position.
  • Step 9.1. Clean carbon deposits: Use a wire brush and engine cleaner to clean any carbon deposits. And make sure not to scratch the surface where gasket marks are present.
  • Step 9.1. Piston bottom dead center: Now turn the flywheel again, bringing the piston to the bottom dead center, i.e., the lowest position.
  • Step 9.1. Check for scratches: Check for any markings or scratches. If scratches are present, take the engine to the honing machine and hone the scratches. This can be a difficult step if needed, go to an engine repair shop, or ask for help from a professional.

● Step 10: clean the surface below the gasket

The old gasket has left a mark on the head as well as the top of the cylinder. Using a scraper or sandpaper, remove the spot with engine cleaner.

● Step 11: Reinstall new lawnmower gasket

Place the new gasket in place before trying to blow pressurized air through all portions for any leftover or stuck carbon deposits.

● Step 12: Reassemble all the components

Reassemble but keep special care of pushrods and valves. Also, retighten the bolts after giving the machine a test run. Do not overtighten any bolts. Use a torque wrench if needed.

● Step 13: Start the lawnmower and check if any problem persists

Start the lawnmower and check again. If the situation were just a gasket and cleaning, the regular operation would continue.

Related Questions

1. How much does it cost to replace a head gasket on a lawnmower?

The cost of replacing a head gasket can be relatively high if done by a professional mechanic. This is mainly due to the time needed to repair. The head gasket itself is not very expensive, and it does not require costly or specialized equipment. If you do the repair yourself, it will be a lot cheaper as there will be no labor cost.

2. Can a head gasket sealer be used?

Yes, if the gasket is just damaged and a new one is not available, you can use a head gasket sealer. But this fix will not last as long as replacing the head gasket.

Final Remarks

When working on your lawn, a smoothly running engine is a joy to operate. If your machine is older and provides smoke, and does not seem to have the same strength as before, it may help replace gaskets. Checking if you have a blown gasket and fixing it sounds like a challenging job. It is not one of the easiest things you can do, but if you are ok with some DIY, it can save you an expensive trip to a professional.

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